Enhanced Transformer Ratio using A Double Triangular Beam Generated using The Emittance Exchange Technique

The transformer ratio plays a very important and direct role in the efficiency of a collinear wakefield acceleration scheme, but it cannot exceed 2 for the commonly used symmetric drive beam. Appropriate shaping of the temporal profile of the electron bunch can greatly increase the transformer ratio but it is rarely implemented because of the difficulty of manipulating the beam in this fashion. We have developed a method to generate a double triangular beam (i.e. a charge distribution with a saw-tooth-like longitudinal profile) using the Emittance Exchange (EEX) technique. This particular bunch shape is able to enhance the transformer ratio by a factor of ~ 2N, where N is the ratio of total bunch length over the rf wavelength of the excited wakefield. Following this rapid enhancement, R is able to attain almost unbelievably high values, e.g. ~30 when N~5. In Phase I of this project, we will prepare the high transformer ratio experiment at AWA using the new proposed double triangular bunch. Major aspects of this work include optimization of the AWA EEX beamline parameters to generate a double triangular bunch, preparation of the vacuum parts and beam control elements that are needed, and design and fabrication of the dielectric wakefield accelerator used to demonstrate the enhanced transformer ratio. Commercial Applications and Other Benefits: The techniques we propose in this project can overcome conventional limitations on the transformer ratio to obtain significantly higher energy transfer efficiency, leading to a breakthrough in the performance of the beam driven wakefield accelerator, one of the most promising schemes in the category of advanced accelerator concepts for high energy physics research applications.